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[Nagidal]

With your help I have designed and built a moderately successful magma trap in my former Fortress Lancedbrains. It trapped invaders in a hallway, then dropped magma on them, and later water on top of it. Mined out, all worthless things gone in an instant, what remained was just the precious iron.

Spoiler: Sketch of the old magma trap design (click to show/hide)

That was an embark with a shallow magma see deep underground. The problem with it was that it took several iterations of this trap to eliminate the whole siege. Usually only a handful of enemies could be trapped in the chamber of death at a time.

Now with a new fortress we embarked on a magma pipe which starts at the bottom of cavern layer 1 — not too far below three aquifer layers. Any ideas how I could use the generously high magma pipe to destroy a whole siege in one run?

I am trying to design a hallway of death, meandering vertically several z-levels from the bottom to the top. Sort of like a water pump stack does with water, this hallway would do with a long stream of enemies. The trick would of course be that instead of floor tiles, this hallway would have magma-safe grates. Once the marching siege parade is stacked and trapped several z-levels high, I'd drop some magma on them. The troops on the top would not be exposed to magma too long, but I figure they'd die from burning and having tissues melting away. Probably there would not be any casting into obsidian needed. I just need a way how to get rid of a river of magma quickly. Do you think I can drain it quickly if I'd lead it to the maps edge? perhaps having a steep ramp leading down to the map's edge to speed up the magma flow. Would the magma just disappear there like aquifer water does?

[Fleeting Frames]

Well, this is probably the smallest magma pump trap. I think he settled on dozen-tile downstair walking space right above magma sea (acting as drain) with pressure plate built on downstairs by digging the stairs, building floor, building plate, removing floor.

You could also get the whole siege on a series of bridges above each other all above magma pipe, and drop them down on grates or bridges you built while temporarily draining the pipe.

Non-submerged grates will be targeted by trolls, though, so maybe ensure the siege can't access pump's standing tile without being in magma instead. Can provide walkable space via downstairs, and even fill it from below with pressure. Also, if your entire bottom area is drain, you can just drain it back into pipe or into a portable drain as well; the issue for drains is straggling 1/7 magmas.

[mightymushroom]

Perhaps rather than grates using open space at the sides of the path to "guide" the magma.

The walking path is a set of switchback paths connected by stairs at the ends.

The magma path is vertical switchbacks running perpendicular to that through the open spaces.


|≈≈≈|
|≈≈_|
| __|
|__ |
| __|
|__ |
| __|
|__ |
||| |
|||_|

where _ is the walking path seen endwise and the _ is a magma release valve.

Magma will easily flow downward; I don't think invaders would try climbing shortcuts and the magma should reach them even if they do. Then the only place you need to secure any grate is at the very bottom, where I've included a catch basin (too small as pictured?) that no combatant would have reason to path into unless falling or pushed in. A bridge "drain stopper" keeps your grate safe until you are reasonably sure nothing will live long enough to building destroy it.

[Luriant]

My actual magma trap.
███
≡#█   <- Track Stop dumping to the grate above the stairs. Hauling route in the Track Stop waiting for assign a Magma filled minecart.
█>_____   
█X█    <- Hatch cover linked to mechanism in the stairs.
█X█
█X█
[A hundred levels more until SMR]
█X█
█X█████
+<█#%%  <- Pump excess magma out, using grate and ignore Destroyers. A door ready to be locked, connecting to the rest of the fortress.
█^__█    <- Lever linked Steel Menacing Spike over Gold floor (or other high density), bridge to reclaim magma safe goblinite.
█████
[SMR and magma]

The stairs go to the bottom, cross a door and go up to the core of my fortress (and some poultry bait with windows and fortifications).
The magma minecart is enough to melt all the invaders in the stairs (usually 8-20), preventing bad toughts with corpses, but preserving iron-steel.
Close the hatch cover to reclaim the items. You need to remove the wall, put the hatch, link the mechanism, and rebuild the wall. Without adjacent tile in the same Z-level, Building Destroyer can't destroy the hatch.

Even with 200 levels above SMR, i have problems trapping the entire siege, but melting a siege without magma pump stacks and preventing bad thoughts is great in the second year. Another problem is built a stair that don't tocuh the caverns, but the borders of the embark tile have a high probability of bypass caves and passages.

I built this design after thinking about a magma railgun in a hallway, but with 1x1 embarks, i have more space in the Z-level, and the gravity can move the magma without limits.

[Nagidal]

Well, this is probably the smallest magma pump trap. I think he settled on dozen-tile downstair walking space right above magma sea (acting as drain) with pressure plate built on downstairs by digging the stairs, building floor, building plate, removing floor.

You could also get the whole siege on a series of bridges above each other all above magma pipe, and drop them down on grates or bridges you built while temporarily draining the pipe.

Non-submerged grates will be targeted by trolls, though, so maybe ensure the siege can't access pump's standing tile without being in magma instead. Can provide walkable space via downstairs, and even fill it from below with pressure. Also, if your entire bottom area is drain, you can just drain it back into pipe or into a portable drain as well; the issue for drains is straggling 1/7 magmas.

I don't understand vjek's mini goblin melter from what he drew. I understand Pseudo's explanation, but I think building destroyers would simply destroy the pump standing next to the pressure plate. Also, how would you stack such trapped pumps up?

As for your other suggestion, with siege dropping on grates immersed in magma pipe. Here, too, I assume, the stacked retracting bridges would be vulnerable to building destroyers. But probably the evil forces don't allow their building destroyers to destroy a building if their access to the fort depends on it, right?

[Nagidal]

█X█    <- Hatch cover linked to mechanism in the stairs.

Please explain "Hatch cover linked to mechanism in the stairs" 

[Nagidal]

Perhaps rather than grates using open space at the sides of the path to "guide" the magma.

The walking path is a set of switchback paths connected by stairs at the ends.

The magma path is vertical switchbacks running perpendicular to that through the open spaces.


|≈≈≈|
|≈≈_|
| __|
|__ |
| __|
|__ |
| __|
|__ |
||| |
|||_|

where _ is the walking path seen endwise and the _ is a magma release valve.

Magma will easily flow downward; I don't think invaders would try climbing shortcuts and the magma should reach them even if they do. Then the only place you need to secure any grate is at the very bottom, where I've included a catch basin (too small as pictured?) that no combatant would have reason to path into unless falling or pushed in. A bridge "drain stopper" keeps your grate safe until you are reasonably sure nothing will live long enough to building destroy it.

Thanks, this is much more along the lines of what I was thinking of. I quickly realized I can't let invaders walk on grates. They could destroy them. I figured I'd need regular floor with open space to one side of it. Having this open space alternating between left and right side of the vertically stacked path into the fortress is much more efficient than my plan of opening a dozen of z-levels of the magma pipe simultaneously and let it wash away the siege to the open space drain on one side. That's something I can easily grasp. However, I need to think how you'd design the catch basin and the drain stopper bridge.

[Fleeting Frames]

They don't have access to the pump's walkable tile (due the pump's impassable tile blocking it), and building destroyers must have be able to stand on a tile adjacent to building to destroy it. Using this you can make, for example, building destroyer safe doors. (Oh yeah, forgot to mention: Every tile of the walking space had an adjacent pump, to incinerate whole squad at once to get around the "leader dead, lets just stand here" bug.)

Stacking those, well you would either have to alternate pumping direction or have magma fall from top level as Luriant describes while alternating one or other end having up/downstairs.

For the other one while sieging trolls will totally destroy anything a BD would if not currently in combat mode (to potentially deadly results, I expect, with floating hive or bookcase which provide walkable surface), but bridges, traps and some other things won't be targeted by building destroyers. Though if they have any ogres or other large beasts the bridges' size limit comes into play.

I expect hatch cover linked to mechanism in the stairs to be as I described just before, or otherwise obsidian-cast pressure plate.

[Nagidal]

They don't have access to the pump's walkable tile (due the pump's impassable tile blocking it)

So you would not exactly stack this vertically. Just build ten such pumps in a row, with all their hatches linked to the single pressure plate, right?

and building destroyers must have be able to stand on a tile adjacent to building to destroy it. Using this you can make, for example, building destroyer safe doors.

How can this allow for BD-safe doors? As far as I experienced, if a BD can stand next to a door, he can destroy it.

For the other one while sieging trolls will totally destroy anything a BD would if not currently in combat mode (to potentially deadly results, I expect, with floating hive or bookcase which provide walkable surface), but bridges, traps and some other things won't be targeted by building destroyers.

Thanks for mentioning that. I misunderstood the wiki, I thought they could destroy raising bridges when they were in their lowered state.

I expect hatch cover linked to mechanism in the stairs to be as I described just before, or otherwise obsidian-cast pressure plate.

Wait, wait, wait. I wasn't aware we are talking about obsidian-cast pressure plates here. I understand how you described building a floor over a downstair, contructing a plate on the floor, then deconstructing that floor. Plate would magically stay there or somehow fall on the downstair where it cannot be constructed. But casting them into obsidian?

So what about the process of draining the magma off the map. Is that possible? Or how else do you get rid of large amounts of magma?

[Luriant]

█X█    <- Hatch cover linked to mechanism in the stairs.

Please explain "Hatch cover linked to mechanism in the stairs" 

Tested with clowns. All stair filled with clowns, with no other distraction, and nobody attack the Hatch Cover. The lever can cut the flow of clowns in the stairs. Open or Close, the Hatch cover is untouchable with walkeable tile orthogonally adjacent.
As a note, a non-linked door/hatch cover can be controled by the player, but if a enemy move across the door, you loses control of the object until some dwarves move across the door. A mechanism linked object can only be controlated with a lever/pressure plate, is better in zones under enemy control.

Dig/build a 1x1 stair, and dig a tile next to the stair.
████
█X  █
████
Dwarves can move to that tile and build a Hatch cover in the Stair. And link the Hatch to a lever. (non linked door/hatch loses control

Build a wall in the tile, cutting acces to the Hatch cover.
████
█XO█
████

As a simple test, you can't build a Hatch cover in a 1x1 stair surrounded by walls. If you can't build or remove the building, Destroyers can destroy the building. In the 1x1 hatch, the game report a "no access". Diagonal tiles don't solve the problem, only N-S-E-W walkeable tile permit access.

The wiki don't reflect the need of walkable perimeter in the building destroyer page, but i remember see the info about destroyer who ignore valid furniture in the same tile. Something about drop a building destroyer in a 1x1 tile over furniture. I haven't tested myself, but the 1x1 hatch coverprove the concept. As a rule... if a dwarves can't interact, is safe from building destroyer.

I have another design that involve ramp up, Door in the Z+1, and ramp down. If the door is the only walkeable tile in the level, nobody can destroy. I put the ramps in diagonal, if a flying destroyer move the the hole above the ramp, but i haven't tested with flying destroyers, only clowns.
   +    z+1
▲█▲  z 0

view from above
▲█▲
█ +█
===================

- Draining magma of the map.
Smooth a stone in the border of the map.
Carve fortification
The liquid move across the fortification and exit the map (and every moved by water).

- Black Hole Track Stop
Make a 1x1 Track stop, dumping to some wall
Put a Minecart in the Track Stop hauling route
Pump liquid in the tile. When the level is 7/7, the minecart refill 2/7, but dump in the wall.
Because a wall is ocuping the space of the liquid, the liquid is destroyed. The Minecart can remove all liquid.

My design uses 2/7 magma, pumping the magma in the lower level to a little room is enough, evaporation solve the problem. But for every minecart uses, 2 tiles for evaporation are necesary. a 7x7 tile is enough for evaporate the content 25 minecarts, every use can melt 8 or more enemies, is a 200 army (an enemies retreat before lose all the soldiers).

[Fleeting Frames]

1) Yes, vjek used toggled gear assembly instead of hatches (only need 1 link for all the pumps with that, but doesn't work with track stop dumping magma from minecart.)

2) It's on the wiki:
  D
▲W▲ - The door on top of wall is building destroyer safe in this 1-wide tunnel. Admittedly, pump 'central' tile, the walkable tile, being blocked by the impassable one is slightly different case (more like grates).

3) *shrugs* it's fine for goblins, but big stuff will ignore your setup. Maybe have a backup cavein to deconstruct all bridges at once in emergency.

4) Buildings, other than supports (due the floor they create on their and above z-level) and linked up retracting bridges, never fall down in any sense unless being hit by a cavein. You can get floating plates/traps/floodgates/etc. also by building a wall underneath and then removing that, but it will only work on flying/swimming creatures and fluids, not falling creatures or flying minecarts, so the downstairs trick has advantages.

I mentioned the casting trick in case one would want to place the plate deeper into the falling magma tower.

5) Yeah you can drain it smash it pump it dump it into wall etc. I've personally drained a volcano with map edge drain due it overflowing. 1/7 magma will only flow downwards, though, so mind that.

[eerr]

Code: [Select]

W  = walls
%_ = screw pump
M  = magma

Code: [Select]

W
W    W    WMMMMW
W    W %_ WMMMMW
W    F WWMMMMMMW
WWWWWWWWWWWWWWWW

Magma won't flow back up to level where it came from, even when pressurized.

So this drops magma into the center. Also the cistern has large amounts of magma, so the pump pressurizes fairly quick.
That just leaves a small amount of magma to be cleaned out of the F area.

That can be done by pumping it into a large open flat area. Magma evaporates at 1/7, and even two tiles of magma should take only 16 or so tiles for a dumping zone.
Or just pump it back to the cistern it came from, but in reverse.

The Fortification should stop anything even if magma safe. If anything, it would be pushed out.

[Nagidal]

Thank you very much for your input and explanations. I don't think I will be able to try all of them in my current fortress. Which one will I pick now depends on many factors. Most importantly, I have yet do explore the true extent of all caverns as I haven't dug deeper than cavern 1. I currently tend to use Fleeting Frames' or mushroom's suggestion.

[Fleeting Frames]

@err. Small note: Magma does rise when pumped by screw pump, so the hole past the fortification is going to have 2z of magma in it. (this has been used to make magma landmines)

(For the 1/7 spots of magma, could simply use downstairs as floor with some sort of draining device described above.)